1. Field of the Invention
The present invention relates generally to a startup circuit, a capacitive sensor amplification device having the startup circuit, and a startup method for the amplification device and, more particularly, to a startup circuit that is capable of setting the initial startup time of a capacitive sensor amplification device to a short time and to a capacitive sensor amplification device having the startup circuit and a startup method for the amplification device.
2. Description of the Prior Art
A condenser microphone is a microphone for converting sounds into electrical signals according to a variation in the capacitance of a condenser, and is also referred to as a “capacitor microphone.”
In particular, an Electret Condenser Microphone (ECM) is characterized in that an existing post-processing stage may be remarkably simplified and noise interference in analog signals may be eliminated. A capacitor microphone is designed using a capacitive sensor, and the output of the capacitive sensor needs to be amplified.
FIG. 1 is a configuration diagram showing an embodiment of a conventional capacitive sensor amplification device 100. As can be seen in FIG. 1, the conventional capacitive sensor amplification device 100 functions to amplify a signal output from a sensor circuit CS, and includes an impedance unit 110 and an amplification unit 120. The sensor circuit CS includes a capacitive sensor (Cmic), and the amplification unit 120 functions to amplify the output signal of the capacitive sensor Cmic.
The capacitive sensor amplification device 100 is capable of transferring a signal only when the output stage of the capacitive sensor Cmic that is a condenser for a microphone is maintained at a high impedance state. Therefore, the input stage of an integrated circuit that receives the signal from the capacitive sensor Cmic has the impedance unit 110 having high impedance. That is, in the amplification device 100 implemented as an integrated circuit for receiving the signal from the capacitive sensor Cmic, an embodiment of a typical circuit is a structure in which a high impedance resistive component is arranged at the input node of an amplifier AMP so as to maintain the input stage of the amplification device 100 at high impedance and form a Direct Current (DC) bias. Typically, the resistance of a high impedance resistive component is implemented as several Giga ohms (GΩ) to several tens of Giga ohms or more. By such a high impedance value, the bias of the input stage node of the amplification device 100 may be uniformly maintained.
When the above-described high impedance is implemented, a problem arises in that the time for which a DC bias is formed in the initial operation of a circuit is greatly lengthened.
Korean Patent Application Publication No. 10-2012-0122162 (entitled “Electret condenser microphone with variable input impedance pre-amplifier and variable input impedance controlling method of the pre-amplifier”) discloses a method for causing the DC bias level of the input signal of an amplifier to promptly converge on an operating region using a variable impedance element.
That is, Korean Patent Application Publication No. 10-2012-0122162 discloses a method for initially controlling the DC bias level of the input signal of the amplifier using an indirect method. However, there is a need to implement a startup circuit using a more direct, faster, and simpler circuit.